To the "eye" of an X-ray telescope, the universe is totally
different , a violent, vibrant, and ever-changing place.
Temperatures can reach millions of degrees. Objects are
accelerated by gravity to nearly the speed of light and
magnetic fields more than a trillion times stronger than the
Earth's cause some stars to crack and tremble.

NASA's newest space telescope, called the Chandra X-ray
Observatory, will allow scientists from around the world to
obtain unprecedented X-ray images of these and other exotic
environments to help understand the structure and evolution of
the universe. The observatory will not only help to probe these
mysteries, but also will serve as a unique tool to study detailed physics in a laboratory that cannot be
replicated here on Earth , the universe itself.
NASA's Chandra X-ray Observatory has every prospect of
rewriting textbooks and helping technology advance in the
coming decade.

The Chandra X-ray Observatory will provide unique and crucial
information on the nature of objects ranging from comets in our
solar system to quasars at the edge of the observable universe.
The observatory should provide long-sought answers to some
major scientific questions, such as:

What and where is the "Dark Matter" in our universe? The
largest and most massive objects in the universe are galaxy
clusters - enormous collections of galaxies, some like our
own. These galaxies are bound together into a cluster by
gravity. Much of their mass is in the form of an incredibly
hot, X-ray emitting gas that fills the entire space between
the galaxies. Yet, neither the mass of the galaxies, nor
the mass of the hot X-ray gas is enough to provide the
gravity that we know holds the cluster together. X-ray
observations with the Chandra X-ray Observatory will map
the location of the dark matter and help us to identify it.

What is the powerhouse driving the explosive activity in
many distant galaxies? The centers of many distant galaxies
are incredible sources of energy and radiation ,
especially X-rays. Scientists theorize that massive black
holes are at the center of these active galaxies, gobbling
up any material , even a whole star , that passes
too close. Detailed studies with the Chandra X-ray
Observatory can probe the faintest of these active
galaxies, and study not only how their energy output
changes with time, but also how these objects produce their
intense energy emissions in the first place.

Since X-rays are absorbed by the Earth's atmosphere,
space-based observatories are necessary to study these
phenomena. To meet this scientific challenge, the Chandra X-ray
Observatory, NASA's most powerful X-ray telescope, was
launched in July 1999. Complementing two other space
observatories now orbiting Earth , the Hubble Space
Telescope and the Compton Gamma Ray Observatory , this
observatory studies X-rays rather than visible light or gamma
rays. By capturing images created by these invisible rays, the
observatory will allow scientists to analyze some of the
greatest mysteries of the universe.

Named in honor of the late Indian-American Nobel Laureate
Subrahmanyan Chandrasekhar, the observatory was formerly known
as the Advance X-ray Astrophysics Facility. The Chandra X-ray
Observatory was carried into low Earth orbit by the Space
Shuttle Columbia. The observatory was deployed from the
shuttle's cargo bay at 155 miles above the Earth. Two
firings of an attached Inertial Upper Stage rocket and several
firings of its own on-board rocket motors after separating from
the Inertial Upper Stage placed the observatory into its
working orbit.

Unlike the Hubble Space Telescope's circular orbit that
is relatively close to the Earth, the Chandra X-ray Observatory
was placed in a highly elliptical (oval-shaped) orbit. At its
closest approach to Earth, the observatory will be at an
altitude of about 6,000 miles. At its farthest, 86,400 miles,
it travels almost one-third of the way to the Moon. Due to this
elliptical orbit, the observatory circles the Earth every 64
hours, carrying it far outside the belts of radiation that
surround our planet. This radiation, while harmless to life on
Earth, can overwhelm the observatory's sensitive
instruments. The X-ray observatory is outside this radiation
long enough to take 55 hours of uninterrupted observations
during each orbit. During periods of interference from
Earth's radiation belts, scientific observations are not
taken.

The Chandra X-ray Observatory has three major elements. They
are the spacecraft system, the telescope system and the science
instruments.

The Spacecraft System
The spacecraft module contains computers, communication
antennas and data recorders to transmit and receive information
between the observatory and ground stations. The onboard
computers and sensors, with ground-based control center
assistance, command and control the vehicle and monitor its
health during its expected five-year lifetime.

The spacecraft module also provides rocket propulsion to move
and aim the entire observatory, an aspect camera that tells the
observatory its position relative to the stars, and a Sun
sensor that protects it from excessive light. Electrical power
is provided by solar arrays that also charge three
nickel-hydrogen batteries that provide backup power.

The Telescope System
At the heart of the telescope system is the High-Resolution
Mirror Assembly. Since high-energy X-rays would penetrate a
normal mirror, special cylindrical mirrors were created. The
two sets of four nested mirrors resemble tubes within tubes.
Incoming X-rays graze off the highly polished mirror surfaces
and are funneled to the instrument section for detection and
study.

The mirrors of the X-ray observatory are the largest of their
kind and the smoothest ever created. If the surface of the
state of Colorado were as relatively smooth, Pike's Peak
would be less than one inch tall. The largest of the eight
mirrors is almost 4 feet in diameter and 3 feet long.
Assembled, the mirror group weighs more than 1 ton.

The High-Resolution Mirror Assembly is contained in the
cylindrical "telescope" portion of the observatory. The entire
length of the telescope is covered with reflective multi-layer
insulation that assists heating elements inside the unit in
keeping a constant internal temperature. By maintaining a
precise temperature, the mirrors within the telescope are not
subjected to expansion and contraction , thus ensuring
greater accuracy in observations.

The assembled mirrors were tested at NASA's Marshall
Space Flight Center in Huntsville, Ala. Marshall's
world-class X-ray Calibration Facility verified the
mirrors' exceptional accuracy , comparable to the
accuracy required to hit a hole-in-one from Los Angeles to San
Diego. This achievement allows the observatory to detect
objects separated by one-half arc second. This is comparable to
reading the letters of a stop sign 12 miles away.

The Chandra X-ray Observatory represents a scientific leap in
ability over previous X-ray observatories like NASA's
Einstein, which orbited the Earth from 1978 to 1981. With its
combination of large mirror area, accurate alignment and
efficient X-ray detectors, the Chandra X-ray Observatory has
eight times greater resolution and is 20-to-50 times more
sensitive than any previous X-ray telescope.

Science Instruments

Within the instrument section of the observatory, two
instruments at the narrow end of the telescope cylinder will
collect X-rays and study them in various ways. Each of the
instruments can serve as an imager or spectrometer.

A High-Resolution Camera will record X-ray images, giving
scientists an unequaled look at violent, high-temperature
occurrences like the death of stars or colliding galaxies. The
High-Resolution Camera is composed of two clusters of 69
million tiny lead-oxide glass tubes. The tubes are only
one-twentieth of an inch long and just one-eighth the thickness
of a human hair. When X-rays strike the tubes, particles called
electrons are released. As the electrons are accelerated down
the tubes by high voltage, they cause an avalanche of about 30
million more electrons. A grid of electrically charged wires at
the end of the tube detects this flood of particles and allows
the position of the original X-ray to be precisely determined.
The High-Resolution Camera also complements the Charge-Coupled
Device Imaging Spectrometer, described below.

The Chandra X-ray Observatory's Imaging Spectrometer is
also located at the narrow end of the observatory. This
detector is capable of recording not only the position, but
also the color (energy) of the X-rays. The imaging spectrometer
is made up of 10 charge-coupled device arrays. These detectors
are similar to those used in home video recorders and digital
cameras but are designed to detect X-rays. Commands from the
ground allow astronomers to select which of the various
detectors to use. The imaging spectrometer can distinguish up
to 50 different energies within the range the observatory
operates. In order to gain even more energy information, two
screen-like instruments, called diffraction gratings, can be
inserted into the path of the X-rays between the telescope and
the detectors. The gratings change the path of the X-ray
depending on its color (energy) and the X-ray cameras record
the color and position. One grating concentrates on the higher
and medium energies and uses the imaging spectrometer as a
detector , the other grating disperses low energies and is
used in conjunction with the High Resolution Camera.

By studying these X-ray rainbows, or spectra, and recognizing
signatures of known elements, scientists can determine the
composition of the X-ray producing objects, and learn how the
X-rays are produced.

Observatory Operations

The Smithsonian Astrophysical Observatory controls science and
flight operations of the Chandra X-ray Observatory for NASA
from Cambridge, Mass. The Smithsonian manages two
electronically linked facilities , the Operations Control
Center and the Science Center.

The Operations Control Center is responsible for directing the
observatory's mission as it orbits Earth. A control center
team interacts with the observatory three times a day ,
receiving science and housekeeping information from its
recorders. The control center team also sends new instructions
to the observatory as needed, as well as transmit scientific
information from the X-ray observatory to the Science
Center.

The Science Center is an important resource for scientists who
wish to study X-ray emitting celestial objects like quasars and
colliding galaxies. The Science Center will provide user
support to researchers, including science data processing and a
science data archive. The Science Center will work with NASA
and the scientific community to allow public access to the
scientific results.

NASA and Partners

The Chandra X-ray Observatory program is managed by the
Marshall Center for the Office of Space Science, NASA
Headquarters, Washington, D.C. TRW Space and Electronics Group (now NGST)
of Redondo Beach, Calif., is the prime contractor and has
assembled and tested the observatory for NASA. Using glass
purchased from Schott Glaswerke, Mainz, Germany, the
telescope's mirrors were built by Raytheon Optical Systems
Inc., Danbury, Conn. The mirrors were coated by Optical Coating
Laboratory, Inc., Santa Rosa, Calif., and assembled by Eastman
Kodak Co., Rochester, N.Y.

The Chandra X-ray Observatory Charge-Coupled Device Imaging
Spectrometer was developed by Pennsylvania State University,
University Park, Pa., and the Massachusetts Institute of
Technology (MIT), Cambridge. One diffraction grating was
developed by MIT, the other by the Space Research Organization
Netherlands, Utrecht, Netherlands, in collaboration with the
Max Planck Institute, Garching, Germany. The High Resolution
Camera was built by the Smithsonian Astrophysical Observatory.
Ball Aerospace & Technologies Corporation of Boulder,
Colo., developed the aspect camera and the Science Instrument
Module.

Chandra X-ray Observatory Technical
Details

Size

45.3 feet long x 64.0 feet wide (solar arrays deployed)

Weight

10,560 pounds

Life

Minimum 5 years

Orbit

6,000 x 86,400 miles, 64-hour period per orbit

Power

Two 3-panel, silicon solar arrays (2,350 watts). Three
40-amp-hour nickel-hydrogen batteries for power in
eclipse